Many modern and/or emerging applications require at least one device electrode that has not only high electrical conductivity, but high optical transparency as well. Such applications include, but are not limited to, touch screens (e.g., analog, resistive, 4-wire resistive, 5-wire resistive, surface capacitive, projected capacitive, multi-touch, etc.), displays (e.g., flexible, rigid, electro-phoretic, electro-luminescent, electrochromatic, liquid crystal (LCD), plasma (PDP), organic light emitting diode (OLED), etc.), solar cells (e.g., silicon (amorphous, protocrystalline, nanocrystalline), cadmium telluride (CdTe), copper indium gallium selenide (CIGS), copper indium selenide (CIS), gallium arsenide (GaAs), light absorbing dyes, quantum dots, organic semiconductors (e.g., polymers, small-molecule compounds)), solid state lighting, fiber-optic communications (e.g., electro-optic and opto-electric modulators) and microfluidics (e.g., electrowetting on dielectric (EWOD)).
As used herein, a layer of material or a sequence of several layers of different materials is said to be “transparent” when the layer or layers permit at least 50% of the ambient electromagnetic radiation in relevant wavelengths to be transmitted through the layer or layers. Similarly, layers which permit some but less than 50% transmission of ambient electromagnetic radiation in relevant wavelengths are said to be “semi-transparent.”
Currently, the most common transparent electrodes are transparent conducting oxides (TCOs), specifically indium-tin-oxide (ITO) on glass. However, ITO can be an inadequate solution for many of the above-mentioned applications (e.g., due to its relatively brittle nature, correspondingly inferior flexibility and abrasion resistance), and the indium component of ITO is rapidly becoming a scarce commodity. Additionally, ITO deposition usually requires expensive, high-temperature sputtering, which can be incompatible with many device process flows. Hence, more robust, abundant and easily-deposited transparent conductor materials are being explored.
Touch screens are display overlays which may be pressure sensitive (resistive), electrically-sensitive (capacitive), acoustically-sensitive (surface acoustic wave (SAW)) and/or photo-sensitive (infra-red). The effect of such overlays is to allow a display to be used as an input device, with such displays often attached to computers and/or networks. Touch screens typically include a touch panel, a controller and a software driver. The touch panel is a transparent panel with a touch-sensitive surface, which registers touch events and sends these signals to the controller. The controller processes these signals and sends the data to the computers and/or networks, wherein the software driver translates the touch events into computer events.
One problem found in conventional touch screen technologies is that many are only capable of reporting a single point even when multiple objects are placed on the sensing surface. That is, they lack the ability to track multiple points of contact simultaneously. In resistive and capacitive technologies, an average of all simultaneously occurring touch points are determined and a single point which falls somewhere between the touch points is reported. In surface wave and infrared technologies, it is difficult, if not impossible, to discern the exact position of multiple touch points that fall on the same horizontal or vertical lines due to masking. In either case, faulty results are generated.
A related problem found in many conventional touch screen technologies is that they utilize transparent conductive materials that are ill-suited for touch panel functionality. For example, ITO can be an inadequate touch panel solution, given that ITO is relatively brittle and consequently prone to mechanical degradation, in which case faulty results are generated. Additionally, currently-available ITO deposition methods can be limiting in terms of the possible touch screen device architectures enabled thereby.